Fix IB-3875: startup required after enabling extension
Fix IB-3875: startup required after enabling extension

The reason was edf72275b8e0def44dfc7de27890d4b274686710 which
made the background page permanent.

When the extension is installed, onStartup() has already been triggered
and thus the "missing" flag remains true.

cristiano-andrade/chrome-token-signing,open-eid/chrome-token-signing,open-eid/chrome-token-signing,open-eid/chrome-token-signing,cristiano-andrade/chrome-token-signing,metsma/chrome-token-signing,open-eid/chrome-token-signing,open-eid/chrome-token-signing,fabiorusso/chrome-token-signing,cristiano-andrade/chrome-token-signing,fabiorusso/chrome-token-signing,metsma/chrome-token-signing,metsma/chrome-token-signing,metsma/chrome-token-signing,fabiorusso/chrome-token-signing,cristiano-andrade/chrome-token-signing,metsma/chrome-token-signing,fabiorusso/chrome-token-signing